Piezoelectric vibration transducer



BlQ BZE 5H v QR mwamve SEARCH Aug. 3, 1965 J. KRIT; 3,198,970

PIEZOELECTRIC VIBRATION TRANSDUCER Filed June 9, 1961 INVENTOR. JACK KEITZ BY a ATTORNEY United States Patent 3,198,970 PIEZOELECTRIC VIBRATION TRANSDUCER Jack Kritz, Westbury, N.Y., assignor to American Bosch Anna Corporation, a corporation of New York Filed June 9, 1961, Ser. No. 115,988 14 Claims. (Cl. 3108.2)

The present invention relates to vibration transducers and has particular reference to the flexure mode vibrating disc type.

Composite construction of sandwich type vibrators using thin layers of piezoelectric material on opposite sides of an inert resilient body such as a lightweight metal or plastic, for example, are described in copending patent application, Serial No. 36,434 now Pat. No. 3,123,727 filed June 15, 1960 by the inventor. It has been found, however, that a complete layer of piezoelectric material is not required. The only area where piezoelectric material is absolutely necessary is in the region of the nodal circle and the rest of the piezoelectric disc adds nothing to the efficiency of the transducer.

The present invention therefore limits the piezoelectric material to a narrow ring at the nodal circle on each side of the circular insert body. The piezoelectric material is preferably imbedded in annular recesses cut in the surface of the body.

By putting the piezoelectric material in the form of a ring in the region of the nodal circle, the higher density material possessing ferroelectric or piezoelectric property such as a titanate ceramic are removed from seriously loading the lighter disc such as aluminum, magnesium, beryllium or plastics for example. In other words, the important characteristics of the material in the region of the nodal circle is stiffness, while in the center and at the edges, mass is the most important. Therefore, the low density material is used in the center and at the edge where low mass is desired, while the dense and stiff material is confined to the nodal region.

For a more complete understanding of the invention, reference may be had to the accompanying drawing in which FIGURE 1 shows one embodiment of the present invention, and

FIGURE 2 shows another embodiment.

Referring to FIGURE 1, a portion of the transducer has been cut away to reveal its construction in a clearer manner.

The transducer of this invention includes a body 11 of low density inert material such as a lightweight metal or plastic shaped in the form of a thin disc, i.e., thickness is small compared to the radius, as described in Us. patent application S.N. 13,923 filed March 9, 1960. Shallow annular recesses 12 in the top and bottom surfaces of the body 11 are completely filled with piezoelectric material 13 which is securely cemented or bonded to the bottom and sides of the annular recesses 12. Electrical insulating material may be interposed between the body 11 and the cylindrical surfaces of the piezoelectric material 13. The transducer 10 may be mounted in a cylindrical frame 14 by three or more supporting members 15, at least one of which serves as an electrical lead, leaving the edge of the disc 11 free to vibrate. The top of the piezoelectric ring is plated with a good conductor of electricity such as gold and the supporting wires 15 are attached to this surface. When an electrical potential is applied between the piezoelectric rings 13, 13 on opposite sides of the body 10 through electrical leads 15 and 16, the piezoelectric rings expand or contract radially according to their polarization, thereby increasing the area of one surface of the disc and decreasing the area of the opposite surface of the disc, bending the disc into a cup shaped object.

The magnitude of the deformation is minute and is invisible to the naked eye. If the electrical potential alternates, the disc is driven into vibration. When the frequency of alternating potential coincides with the fundamental natural frequency of vibration of the disc 11, the amplitude of vibration is a maximum and the motion takes place about a nodal circle which, according to theory, has a radius equal to about 68 percent of the radius of the disc 11 for thin plates. The inner radius of ring 13 is therefore made less than 68 percent of the radius of disc 11 while the outer radius of ring 13 is greater than 68 percent of the radius of disc 11.

FIG. 2 shows a modification of the transducer 10 in which the piezoelectric material 13 is placed at the bottom of a single annular recess 12 which extends from one surface of body 11 substantially up to the central plane AA of body 11. The outer surface of the body 11 is not cut into. The piezoelectric ring 13 is covered by an annular ring of metal 17 preferably the same metal as that of which the body 11 is made. The metal ring is electrically insulated from the body 11 by an epoxy 18 (which may also insulate the sides of piezoelectric ring 13 from the sides of the recess 12) to provide a continuous upper surface on the disc. The electrical field for activation of the transducer is applied between the supports 15 (which are attached to the lower surface of the body 11) and lead 16 which is attached to ring 17.

The term piezoelectric material must be broadly interpreted so as to include all materials which exhibit dimensional change in the presence of an electrical field such .as quartz crystals, titanate ceramics and other ferroelectric materials, for example. The lightweight body may be aluminum, magnesium, beryllium for example, or any one of a number of available plastics.

It should be realized that the transducer can be used for inducing vibrations into a surrounding medium when activated by an applied electrical field, or can be used to produce electrical signals when vibrations impinge on the surface of the transducer.

I claim:

1. In a device of the character described, a flexure mode, free-edge, vibrating disc of vibration-transmissive inert material, said disc having an annular recess in one major surface thereof, and an annular body of piezoelectric material bonded to said disc in said recess, said annular body being substantially in the region of the nodal circle of said disc for the fundamental mode of flexural vibration thereof, whereby said inert disc is caused to vibrate in flexure upon application of an alternating electrical field to said piezo-electric material.

2. A flexure mode, free-edge, vibrating disc sonic transducer comprising a disc of vibration-transmissive inert material having its periphery free to vibrate and an annular body of piezoelectric material bonded to one of the major surfaces of said disc inwardly of the circular periphery thereof, whereby said inert disc is caused to vibrate in flexure upon application of an alternating electrical field to said piezo-electric material.

3. A flexure mode, free-edge, vibrating disc, sonic transducer comprising a disc of resilient, vibration-transmissive material having an annular recess in one major surface thereof and an annular body of piezoelectric material in said recess and bonded to said disc, said annular body having an inner radius at least as small as substantially 68% of the radius of said disc and an outer radius at least as great as substantially 68% of said radius of said disc.

4. A transducer in accordance with claim 3, in which said recess has a depth of substantially one-half the thickness of said disc.

5. A transducer in accordance with claim 3, in which said annular recess is located substantially in the region of the nodal circle of the fundamental mode of flexural vibration of said disc.

6. A transducer in accordance with claim 3 comprising a metallic ring overlying said annular body.

7. A transducer in accordance with claim 3, in which said body of piezoelectric material substantially fills said recess, and comprising an electrically insulating material between said body of piezoelectric material and the side walls of said recess.

8. A transducer in accordance with claim 3, in which said disc has another annular recess in the surface thereof opposite said annular body, and comprising another annular body of piezoelectric material in said other recess.

9. A transducer in accordance with claim 3, in which said disc is of a material lighter than said piezoelectric material.

10. A transducer in accordance with claim 9, in which said disc is of aluminum.

11. A transducer in accordance with claim 9, in which said body of piezoelectric material is of titanate ceramic.

12. A transducer in accordance with claim 9, in which said body of piezoelectric material is of piezoelectric quartz.

13. A transducer in accordance with claim 3, in which both said recess and said body of piezoelectric material are disposed substantially at the nodal circle of the fundamental mode of fiexural vibration of said disc, in which said recess has a depth substantially equal to onehalf the thickness of said disc, and comprising a ring of metal overlying said body of piezoelectric material, said Wm i A body of piezoelectric material and said ring together substantially filling said recess to a height substantially flush with said major surface of said disc, and also comprising support means for said disc attached between the edges of said recess.

14. A transducer in accordance with claim 13, in which said disc has another annular recess in the surface thereof opposite said body of piezoelectric material, and comprising another annular body of piezoelectric material in and substantially filling said other recess, another ring of metal overlying said other body of piezoelectric material, and electrical insulating means between the sidewalls of each of said annular recesses and said piezoelectric body therein.

References Cited by the Examiner UNITED STATES PATENTS 1,809,624 6/31 Giebe et al 3l09.6 X 1,907,425 5/33 M-arrison 3 l09.6 X 2,509,913 5/50 Espenschied 3 l09.6 X 2,556,558 6/51 Silverman 3l0-9.6 X 2,607,858 8/52 Mason 310-9.6 X 2,900,536 8/59 Palo 310-96 3,093,760 6/ 63 Tarasevich 310- X 3,114,848 12/63 Kritz 310-83 X 3,115,588 12/63 Hueter 310-86 3,123,727 3/64 Kritz 318-82 MILTON O. HIRSHFIELD, Primary Examiner.

JOHN F. COUCH, Examiner. 

1. IN A DEVICE OF THE CHARACTER DESCRIBED, A FLEXURE MODE, FREE-EDGE, VIBRATING DISC OF VIBRATION-TRANSMISSIVE INERT MATERIAL, SAID DISC HAVING AN ANNULAR RECESS IN ONE MAJOR SURFACE THEREOF, AND AN ANNULAR BODY OF PIEZOELECTRIC MATERIAL BONDED TO SAID DISC IN SAID RECESS, SAID ANNULAR BODY BEING SUBSTANTIALLY IN THE REGION OF THE NODAL CIRCLE OF SAID DISC FOR THE FUNDAMENTAL MODE OF FLEXURAL VIBRATION THEREOF, WHEREBY SAID INERT DISC IS CAUSED TO VIBRATE IN FLEXURE UPON APPLICATION OF AN ALTERNATING ELECTRICAL FIELD TO SAID PIEZO-ELECTRIC MATERIAL. 